Atomic layer deposition (ALD) of nanoscale coatings on SrAl ₂ O ₄ ‐based phosphor powders to prevent aqueous degradation

Abstract

Abstract The aqueous degradation of Eu 2+ ‐activated and Dy 3+ ‐codoped strontium aluminate (SrAl 2 O 4 :Eu 2+ , Dy 3+ , SA2‐Green) long afterglow phosphors synthesized from solid‐state reaction and coated with nanoscale metal oxide protective layers (≤12 nm) via atomic layer deposition (ALD) is investigated. Uncoated phosphor powders degrade rapidly upon water immersion and lose their green phosphorescence within 48 hours of water exposure. Postmortem investigations reveal hydration and decomposition of the SrAl 2 O 4 phase. ALD of ~10 nm Al 2 O 3 or ~12 nm TiO 2 is found to significantly improve the powder's resistance to aqueous degradation. All ALD‐coated powders show minimal structural and chemical degradation and retain phosphoresence after 48 hours of water immersion. This enhanced durability offers a new pathway for applying long afterglow phosphors to outdoor applications like roadway markings or safety signage and for their incorporation into more eco‐friendly waterborne coatings.